1. Field of the Invention
The present invention relates to a receiver for receiving broadcast waves, and more particularly to a receiver, which is provided with a database having broadcasting station related information for identifying broadcasting stations, the type of broadcast programs and so on, for receiving RBDS (Radio Broadcasting Data System) broadcast waves in which a main information signal such as an audio signal and an information data signal related to a broadcasting station transmitting the main information signal are multiplexed.
2. Description of the Related Art
The RBDS in the United States is similar to the RDS (Radio Data System) practically used in Europe. Specifically, on the transmitter side, additional control signals such as a PI (Program Identification) code for identifying a broadcasting station, a PTY (Program Type) code for identifying or classifying a broadcast program, and so on are frequency-division-multiplexed on an audio signal constituting a main information signal to generate transmission waves (broadcast waves). Then, on the receiver side, these codes are read from received broadcast waves, so that a variety of controls can be carried out in accordance with the contents of the read codes. Other than such receivers relying upon the RBDS broadcast waves, there is also a database type receiver which has a previously prepared database including identification data for identifying broadcasting stations, the type of broadcast programs, and so on, respectively expected to be received. In detail the identification data is stored in a non-volatile memory such as a ROM (Read-Only Memory) as the broadcasting station related information in association with reception frequencies and reception areas (for example, individual areas defined by dividing the entire territory of the United States at intervals of 0.5 degrees both on the latitude and on the longitude. The divided area is called "grid") to form the database. In the database type receiver, the memory is accessed, upon actually receiving broadcast waves, to read out information indicative of a grid corresponding to a reception position of the receiver, broadcasting station corresponding to a preset reception frequency and the type of a received broadcast program. On the basis of the read information, displaying is performed with respect to the name of the broadcasting station (for example, a call sign) and the type of the received broadcast program (for example, a rock program, a jazz program, a news program and so on. The information indicative of the program type is called "format"). The receiver furthermore performs to select a broadcasting station emitting a type of a broadcast program desired by a user. Such a type of receiver is described, for example, in Laid-open Japanese Patent Application No. 1-117529(1989).
In recent years, there have been further proposed a database type RBDS receiver which utilizes dedicated update data available from RBDS broadcast waves. According to this receiver, the stored data of a database memory is supplemented such that broadcasting station related information can be acquired in accordance with an actual receiving condition or receiving environment. More specifically, supplementary broadcasting station related information supplied from update data is stored into a database supplementary memory such as a RAM provided in the receiver separately from the database memory, such that a variety of proper controls are carried out using integrated data information including supplementary data stored in the supplementary memory and original data stored in the database memory. This proposal has been made, for example, in "UNITED STATES RBDS STANDARD FOR BROADCAST DATA SYSTEMS, DRAFT NO. 1.4 NRSC DOCUMENT, Jan. 10, 1992," and particularly, "3.1.3.6 Type 5 groups: Transparent data channels" from page 22 in the document treats the above-mentioned configuration.
In the receiver which supplements the database using the update data as mentioned above, the database supplementary memory is controlled for writing data only when RBDS broadcast waves having update data are received by the receiver. However, it can be thought that the update data is emitted from an associated broadcasting station later than the time the contents of broadcast programs are actually updated, in which case, the receiver is forced to use an old version of broadcasting station related information for control, so that the receiver is obliged to perform improper control not adapted to the recent broadcast contents.